Add repo name to worktree path (#7)

This addresses two issues: 1) no longer assume that the user is working
from the root directory of the repository, and 2) put the repo name in
the working tree path to avoid any potential conflicts from backports
from other repositories.

Signed-off-by: Andrew Ross <andrross@amazon.com>

src/backport.ts

@@ -157,20 +157,24 @@ const getFailedBackportCommentBody = ({
   commitSha,
   errorMessage,
   head,
+  repo,
 }: {
   base: string;
   commitSha: string;
   errorMessage: string;
   head: string;
+  repo: string;
 }) => {
-  const worktreePath = `../.worktrees/backport-${base}`;
+  const worktreePath = `../.worktrees/${repo}/backport-${base}`;
   return [
     `The backport to \`${base}\` failed:`,
     "```",
     errorMessage,
     "```",
     "To backport manually, run these commands in your terminal:",
     "```bash",
+    "# Navigate to the root of your repository",
+    "cd $(git rev-parse --show-toplevel)",
     "# Fetch latest updates from GitHub",
     "git fetch",
     "# Create a new working tree",
@@ -329,6 +333,7 @@ const backport = async ({
               commitSha: mergeCommitSha,
               errorMessage: error.message,
               head,
+              repo
             }),
             issue_number: number,
             owner,